Plasma sources for spectrochemical analysis sometimes include a plasma torch coupled to an electromagnetic waveguide so that electromagnetic radiation (e.g., microwave radiation) can be used to generate and sustain the plasma.
One known type of plasma source includes a waveguide so oriented that the magnetic field of the electromagnetic radiation is oriented along a common axis of the plasma torch, and the magnetic field strength is at a maximum at the position of the plasma torch. This type of plasma source ideally establishes a plasma having a circular or elliptical cross-section, and with a slightly less dense (cooler) plasma along the axial dimension.
While that known plasma source provided significant improvement over other known plasma sources, the performance of the plasma source was found to be compromised if the length of the waveguide deviated even by small amounts from the optimum. Notably, minor variations in the length of the waveguide, as can be expected to occur in a routine manufacturing environment, were found to result in the establishment of undesirable asymmetric plasmas, that adversely affect the analytical performance of the plasma source.
There is therefore a need to provide an improved electromagnetic waveguide and plasma source that overcomes at least the shortcomings of the known waveguides and plasma sources described above.